1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to an apparatus for removing bubbles from a sealant for fabricating a liquid crystal display device. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for reliably forming a sealant on the substrates.
2. Discussion of the Related Art
A thin flat panel display tends to have a thickness no more than a few centimeters. Particularly, the liquid crystal display device has a wide scope of application, such as portable computers, television and computer monitors, and gauge monitors for spaceships and airplanes due to a low driving voltage, a low consumption power, and a portability.
As shown in FIG. 1, a liquid crystal display device generally includes a lower substrate 1 having a thin film transistor and a pixel electrode, an upper substrate 3 facing into the lower substrate 10 and having a light shielding film, a color filter layer, a common electrode, and a liquid crystal layer 5 interposed between both the upper and lower substrates 3 and 1.
A sealant 7 is formed between the upper and lower substrates 3 and 1 to prevent the liquid crystal 5 from leaking and to bond the upper and lower substrates 3 and 1 to each other.
A method of fabricating the liquid crystal display device having the above-described structure is classified into a vacuum injection method and a liquid crystal dropping method, depending upon the method of forming the liquid crystal layer between the upper and lower substrates.
A method of fabricating the liquid crystal display device according to the vacuum injection method will now be described.
A lower substrate having a thin film transistor and a pixel electrode, and an upper substrate having a light shielding film, a color filter layer, and a common electrode are prepared.
A sealant is dispensed to either of the upper and lower substrates to prevent the liquid crystal from leaking and to attach the lower and upper substrates to each other. A thermo-hardening sealant formed of epoxy resin or the like may be used to attach the substrates.
After attaching the upper and lower substrates to each other, the thermo-hardening sealant is hardened by a heating process to bond the upper and lower substrates to each other.
After the bonded substrates are loaded into a vacuum chamber and the inner space between the substrates is maintained at a vacuum condition, the bonded substrates are dipped in a vessel containing a liquid crystal to form a liquid crystal layer between the bonded substrates.
However, the vacuum injecting method has a drawback in that, as a display screen becomes larger in size, a time required for injecting the liquid crystal is extended, thereby reducing productivity.
The liquid crystal dropping method is used to resolve such problems and disadvantages. The steps of preparing upper and lower substrates, forming a spacer, and dispensing a sealant are similar to those in the vacuum injecting method.
In the liquid crystal dropping method, the step of dropping the liquid crystal within the boundary of the sealant formed on the lower substrate is carried out before the step of attaching the substrates to each other.
In other words, the liquid crystal dropping method includes the attaching step of the both substrates after dropping the liquid crystal. When the thermo-hardening sealant is used, the sealant is molten and flows into the liquid crystal during a heating process, thereby contaminating the liquid crystal. For this reason, the liquid crystal dropping method employs a photo-hardening sealant made of acrylic resin.
Accordingly, after the step of attaching the substrates, the substrates are bonded to each other by irradiating UV-ray onto the substrates.
When the thermo-hardening sealant or the photo-hardening sealant used in the vacuum injecting method or the liquid crystal dropping method is made of epoxy resin or acrylic resin only, it has to be fully compressed between the substrates during the attaching step. Thus, a cell gap cannot be maintained. Accordingly, the epoxy resin or acrylic resin is mixed with glass fiber in order to maintain a uniform cell gap.
Since the sealant is mixed with glass fiber, bubbles are formed within the sealant. So, when the sealant having bubbles is dispensed on either the upper substrate or the lower substrate, openings are formed at the portion containing the bubbles, thereby reducing the adhesion of the attached substrates.
Therefore, a step of removing the bubbles of the sealant is carried out before the sealant is dispensed onto the substrate.
FIG. 2A is a partial-cut perspective view of a related art apparatus for removing bubbles from the sealant.
As shown in FIG. 2A, the related art apparatus for removing bubbles from the sealant includes a drum 10, a rotating shaft 20 formed in the drum 10, and a bubble removing container 30.
A first gear 22 is formed at an upper portion of the rotating shaft 20. A second gear 32 is formed at an upper portion of the bubble removing container 30. Herein, the first gear 22 matches the second gear 32.
Accordingly, as the rotating shaft 20 rotates, the bubble removing container 30 and the drum 10 also rotate along with the rotating shaft 20. As the drum 10 rotates, the bubble removing container 30 rotates in large circles.
According to the above-described structure, the sealant is introduced into the bubble removing container 30, whereby the bubble removing container 30 rotates to remove bubbles from the sealant.
FIG. 2B is an enlarged view of the related art bubble removing container 30 having a simple beaker shape and a discharge port for discharging the sealant at the bottom portion.
Generally, since the sealant has a high viscosity, the temperature of the sealant rises due to friction with the inner wall of the bubble removing container 30 during the rotation of the container 30. The rise in temperature changes the characteristics of the sealant.